1. Field of the Invention
This invention relates to ultrasonic motors and to vibration detection methods for ultrasonic motors.
This application is based on Japanese Patent Application No. 2006-216710, the content of which is incorporated herein by reference.
2. Description of Related Art
Recently, ultrasonic motors have been drawing attention as a new type of motor replacing electromagnetic motors. Ultrasonic motors have the following advantages over known electromagnetic motors:    1) Ultrasonic motors are capable of high torque without using gears;    2) Ultrasonic motors have holding force when powered off;    3) Ultrasonic motors have high resolution;    4) Ultrasonic motors are quiet; and    5) Ultrasonic motors do not generate magnetic noise and are unaffected by noise.
A known ultrasonic motor is described in Japanese Unexamined Patent Application, Publication No. HEI-7-193291. In this ultrasonic motor, internal electrodes for detecting vibrations are provided on some layered piezoelectric elements, which enable vibrations to be detected.
However, the vibration which can be detected using the ultrasonic motor described in Japanese Unexamined Patent Application, Publication No. HEI-7-193291 is only a flexural vibration generated in a cylindrical rod-shaped vibrator. Accordingly, in a vibrator that simultaneously generates a longitudinal vibration and a flexural vibration, each vibration cannot be independently detected using the internal electrodes disclosed in Japanese Unexamined Patent Application, Publication No. HEI-7-193291; this is a problem because a separate, special device is thus required.